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<h1>Comma Separated Value (.csv)</h1>

<p>OGR supports reading and writing primarily non-spatial tabular data stored in
text CSV files.  CSV files are a common interchange format between 
software packages supporting tabular data and are also easily produced
manually with a text editor or with end-user written scripts or programs.</p>

<p>While in theory .csv files could have any extension, in order to
auto-recognise the format OGR only supports CSV files ending with the
extention ".csv".  The datasource name may be either a single CSV file
or point to a directory.  For a directory to be recognised as a .csv datasource
at least half the files in the directory need to have the extension .csv.
One layer (table) is produced from each .csv file accessed.</p>

<p> Starting with GDAL 1.8.0, for files structured as CSV, but not ending with
.CSV extension, the 'CSV:' prefix can be added before the filename to force
loading by the CSV driver.</p>

<p>The OGR CSV driver supports reading and writing. Because the CSV format 
has variable length text lines, reading is done sequentially. Reading 
features in random order will generally be very slow. OGR CSV layer never
have any coordinate system.  When reading a field named "WKT" is assumed
to contain WKT geometry, but also is treated as a regular field.
The OGR CSV driver returns all attribute columns as string data types
if no field type information file (with .csvt extension) is
available.</p>

<p>Limited type recognition can be done for Integer, Real, String, Date 
(YYYY-MM-DD), Time (HH:MM:SS+nn) and DateTime (YYYY-MM-DD HH:MM:SS+nn) columns
through a descriptive file with the same name as the CSV file, but a .csvt extension.
In a single line the types for each column have to be listed with double quotes and
be comma separated (e.g., "Integer","String"). It is also possible to specify
explicitly the width and precision of each column, e.g. "Integer(5)","Real(10.7)","String(15)".
The driver will then use these types as specified for the csv columns.</p>

<h2>Format</h2>

<p>CSV files have one line for each feature (record) in the layer (table).  
The attribute field values are separated by commas. At least two fields
per line must be present. Lines may be terminated by a DOS (CR/LF) or
Unix (LF) style line terminators. Each record should have the same number
of fields. Starting with GDAL 1.7.0, the driver will also accept a semicolon
or a tabulation character as field separator . This autodetection will work only
if there's no other potential separator on the first line of the CSV file.
Otherwise it will default to comma as separator.</p>

<p>Complex attribute values (such as those containing commas, quotes or newlines) 
may be placed in double quotes. Any occurances of double quotes within 
the quoted string should be doubled up to "escape" them.</p>

<p>The driver attempts to treat the first line of the file as a list of field 
names for all the fields. However, if one or more of the names is all 
numeric it is assumed that the first line is actually data values and
dummy field names are generated internally (field_1 through field_n) and
the first record is treated as a feature. Starting with GDAL 1.9.0 
numeric values are treated as field names if they are enclosed in double quotes. 
</p>

<p>All CSV files are treated as UTF-8 encoded. Starting with GDAL 1.9.0, a Byte
Order Mark (BOM) at the beginning of the file will be parsed correctly. From 1.9.2,
The option WRITE_BOM can be used to create a file with a Byte Order Mark, which can 
improve compatibility with some software (particularly Excel).
</p>

Example (employee.csv):
<pre>
ID,Salary,Name,Comments
132,55000.0,John Walker,"The ""big"" cheese."
133,11000.0,Jane Lake,Cleaning Staff
</pre>

<p>Note that the Comments value for the first data record is placed in 
double quotes because the value contains quotes, and those quotes have
to be doubled up so we know we haven't reached the end of the quoted string
yet.</p>

<p>Many variations of textual input are sometimes called Comma Separated
Value files, including files without commas, but fixed column widths,
those using tabs as separators or those with other auxiliary data defining
field types or structure. This driver does not attempt to support all 
such files, but instead to support simple .csv files that can be 
auto-recognised. Scripts or other mechanisms can generally be used to convert
other variations into a form that is compatible with the OGR CSV driver.</p>

<h2>Reading CSV containing spatial information</h2>

<p>It is possible to extract spatial information (points) from a CSV file
which has columns for the X and Y coordinates, through the use of the
<a href="drv_vrt.html">VRT</a> driver.</p>

<p>Consider the following CSV file (test.csv):
<pre>
Latitude,Longitude,Name
48.1,0.25,"First point"
49.2,1.1,"Second point"
47.5,0.75,"Third point"
</pre>

You can write the associated VRT file (test.vrt):
<pre>
&lt;OGRVRTDataSource&gt;
    &lt;OGRVRTLayer name="test"&gt;
        &lt;SrcDataSource&gt;test.csv&lt;/SrcDataSource&gt;
        &lt;GeometryType&gt;wkbPoint&lt;/GeometryType&gt;
        &lt;LayerSRS&gt;WGS84&lt;/LayerSRS&gt;
        &lt;GeometryField encoding="PointFromColumns" x="Longitude" y="Latitude"/&gt;
    &lt;/OGRVRTLayer&gt;
&lt;/OGRVRTDataSource&gt;
</pre>
</p>

and <i>ogrinfo -ro -al test.vrt</i> will return :
<pre>
OGRFeature(test):1
  Latitude (String) = 48.1
  Longitude (String) = 0.25
  Name (String) = First point
  POINT (0.25 48.1 0)

OGRFeature(test):2
  Latitude (String) = 49.2
  Longitude (String) = 1.1
  Name (String) = Second point
  POINT (1.1 49.200000000000003 0)

OGRFeature(test):3
  Latitude (String) = 47.5
  Longitude (String) = 0.75
  Name (String) = Third point
  POINT (0.75 47.5 0)
</pre>

<h2>Creation Issues</h2>

<p>The driver supports creating new databases (as a directory
of .csv files), adding new .csv files to an existing directory or .csv
files or appending features to an existing .csv table. Deleting or
replacing existing features is not supported.</p>

<p>Layer Creation options:

<ul>
<li><b>LINEFORMAT</b>: By default when creating new .csv files they are created with the line
termination conventions of the local platform (CR/LF on win32 or 
LF on all other systems).  This may be overridden through use of the
LINEFORMAT layer creation option which may have a value of <b>CRLF</b>
(DOS format) or <b>LF</b> (Unix format).</li><p>
<li><b>GEOMETRY</b> (Starting with GDAL 1.6.0): By default, the geometry of a feature written to a .csv
file is discarded. It is possible to export the geometry in its WKT representation by specifying
GEOMETRY=<b>AS_WKT</b>. It is also possible to export point geometries into their X,Y,Z components (different
columns in the csv file) by specifying GEOMETRY=<b>AS_XYZ</b>, GEOMETRY=<b>AS_XY</b> or GEOMETRY=<b>AS_YX</b>.
The geometry column(s) will be prepended to the columns with the attributes values.</li><p>
<li><b>CREATE_CSVT</b>=YES/NO (Starting with GDAL 1.7.0): Create the associated .csvt file (see above paragraph)
to describe the type of each column of the layer and its optional width and precision. Default value : NO</li><p>
<li><b>SEPARATOR</b>=COMMA/SEMICOLON/TAB (Starting with GDAL 1.7.0): Field separator character. Default value : COMMA</li><p>
<li><b>WRITE_BOM</b>=YES/NO (Starting with GDAL >1.9.2): Write a UTF-8 Byte Order Mark (BOM) at the start of the file. Default value : NO</li><p>
</ul>
</p>

<h2>VSI Virtual File System API support</h2>

(Some features below might require OGR &gt;= 1.9.0)<p>

The driver supports reading and writing to files managed by VSI Virtual File System API, which include
"regular" files, as well as files in the /vsizip/ (read-write) , /vsigzip/ (read-only) , /vsicurl/ (read-only) domains.<p>

Writing to /dev/stdout or /vsistdout/ is also supported.<p>

<h3>Examples</h3>

<ul>
<li> This example shows using ogr2ogr to transform a shapefile with point geometry into a .csv file with the X,Y,Z coordinates of the points as first columns in the .csv file
<pre>ogr2ogr -f CSV output.csv input.shp -lco GEOMETRY=AS_XYZ</pre>
</li>
</ul>

<h2>Particular datasources</h2>

The CSV driver can also read files whose structure is close to CSV files :
<ul>
<li>Airport data files NfdcFacilities.xls, NfdcRunways.xls, NfdcRemarks.xls and NfdcSchedules.xls
    found on tha <a href="http://www.faa.gov/airports/airport_safety/airportdata_5010/menu/index.cfm">FAA website</a> (OGR &gt;= 1.8.0)</li>
<li>Files from the <a href="http://geonames.usgs.gov/domestic/download_data.htm">USGS GNIS</a> (Geographic Names Information System) (OGR &gt;= 1.9.0)</li>
<li>The allCountries file from <a href="http://www.geonames.org">GeoNames</a> (OGR &gt;= 1.9.0 for direct import)</li>
<li><a href="http://epp.eurostat.ec.europa.eu/NavTree_prod/everybody/BulkDownloadListing?file=read_me.pdf">Eurostat .TSV files</a> (OGR &gt;= 1.10.0)</li>
</ul>

<h2>Other Notes</h2>

<p>
<ul>
<li>Development of the OGR CSV driver was supported by 
<a href="http://www.dmsolutions.ca/">DM Solutions Group</a> and 
<a href="http://www.gomoos.org/">GoMOOS</a>.
</ul>
</p>

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